Thermal switch



April '1, 1942.

c l. HALL THERMAL SWITCH Filed Oct. 21, 1941 1 liq vv z Inventor: Ch estew" I. H 8| His Attorn ey.

Illlllll" lgwunnlq l Patented Apr. 7, 1942 THERMAL SWITCH Chesterl.Hall, Bexford, N. Y., assignor to General Electric Company, acorporation of New York Application October 21, 1941, Serial No. 415,929

' (c1. Mil-122) K Claims.

My invention relates to thermal switches and particularly to manually orautomaticallyreset thermo-responsive relays for interrupting an electriccircuit in response to excessive heat developed by a predeterminedexcessive current flowing therethrough.

One of the principal objects of my invention is to provide a new andimproved relay of the above character which is simple and inexpensive tomanufacture and which will give long and dependable service witha-minimum of attention.

It is a further object of my invention to provide a relay of the abovecharacter which is rugged in construction and which will accuratelymaintain its temperature adjustment despite considerable rough usage.

It is a still further object of my invention to provide such a thermalrelay with a snap action in opening and closing its contacts and with asimple and easily accessible means to change over the relay from manualto automatic reset operation.

It is a specific object of my invention to provide a thermal relayhaving a snap acting movable switch member arranged to disengage thecontacts with a hammer blow.

rear side elevation of the device in Fig. 1; Fig. 4 is a sectional viewtaken along the lines 4-4 of Fig. 1; and Fig. 51s a sectional view takenalon the lines 5-5 of Fig. 1.

Referring now to the drawing, I have shown my thermal relay supportedwithin a box-like base In of suitable insulating material, such as amolded plastic compound. The sides of the insulating base iii areirregularly shaped and provided with a plurality of bosses, bores,slots, and the like to accommodate the various parts of the operatingmechanism, as will be more fully de- To the attainment of the above andother objects of my invention I provide a movable switch member, springpressed into pivotal engagement with a pair of substantially parallelrods mounted upon .a suitable base. The rods are made of materialshaving substantially diiferent temperature coefficients of expansion,and means are provided for heating the rod having the higher coefllcientof expansion in response to the magnitude of the current flowing in acircuit to be protected. Unequal-expansion or contraction of thesupporting rods causes pivotal movement of the contact carrying movableswitch member and consequent opening or closing of a pair of circuitcontrolling contacts. Preferably, the movable switch member also carriesa keeper of magnetic material cooperable with a small permanent magnetof high coercive force for the purpose of endowing the contact movementwith snap action in both directions. 7

My invention itself will be better understood and its objects andadvantages further appreciated by referring now to the followingdetailed specification taken in conjunction with the accompanyingdrawing, in which Fig. 1 is a side view, partly in section, of a thermalswitch embodying my invention, the casing cover being removed todisclose the operating parts; Fig. 2 is a plan view of the device ofFig. 1; Fig. 3 is a scribed hereinafter. Adjustably threaded into oneside of the casing III is a rod ll having a substantially spherical endI! arranged to support a right angular switch member or contact arm l3having a complementally shaped recess I4 engaging the spherical end l2of the rod I l.

. As shown, the rod H is threaded into a metallic bushing I 5' which isin turn threaded into a tapped hole in the side of the casing l0. Tomaintain the supporting rod II in laterally fixed position, the casingI0 is preferably provided with a pair of integrally formed upstandingbosses l6 and I1 spaced apart just sufiiciently to permit interpositionof the rod. I Disposed substantially parallel to the rod II andextending between the switch arm l3 and the side of the casing I0 is asecond rod l8 having" conically shaped'end portions arranged forpinpoint engagement with both the switch arm l3 and the side of thecasing Ill. The switch arm i3 is biased into engagement with both therods II and I8 by means of an arcuate spring strip l8 positioned betweenthe switch arm l3 and an opposite side of the base It. Preferably, thesupporting rod II is formed of a metallic alloy having an exceedinglysmall temperature coeflicient of expansion, while the temperaturesensitive rod I8 is formed of a metal having a relatively largetemperature coefllcient of expansion. For example, a suitable materialfor the supporting rod is an alloy composed of approxir mately 36 percent nickel, 0.2 per cent carbon,

and the remainder iron, while a suitable material for the expansible rodI8 is aluminum. Although in the preferred form of my invention thesupporting rod II is substantially no'nexpansible, I wish it to beunderstood that my invention is not limited to such an arrangement, forit will be evident to those skilled in the art that the 1 device willoperate entirely satisfactorily so long as the temperature coeflicientof expansion of the supporting rod H is substantially smaller than thetemperature coeflicient of expansion of the expansible rod i5.

The switch member I3 is in the form of a substantially right angularlever having a transverse rigid portion 25 disposed substantially atright angles to the rods II and |5. and a channelshaped metallic rigidportion 2| disposed substantially parallel to the rods. Connected to therigid portion 29 of the lever by means of a bolt 22, I also provide apair of cantilever leaf springs 23 and 24 arranged in substantiallyparallel spaced relation to the rigid portion 2|. The leaf spring 23 is.a contact spring carrying at its outer extremity a movable contact 25arranged in normal engagement with a stationary contact 25. The leafspring 24 is an armature spring and arranged to carry at its outer end akeeper 21 of magnetic material for cooperation with a small permanentmagnet 28. The rigid portion 2| of the switch member is shorter than thearmature spring 24 and has at its end an in-turned projection 2|aarranged to engage the armature spring adjacent the magnet keeper 21.Similarly, the armature spring is shorter than the contact spring 23 andcarries at its end an in-turned projection 24a arranged to engage thecontact spring 23 adjacent the contact 25.

piece or spring wir 52.

The snap action magnet 25 is preferably of the type exerting arelatively high coercive force in proportion to the physical dimensionsof the magnet. While I do not wish to be limited thereto, a suitablematerial, and one which I prefer to use for the magnet, is an alloycomprising of 6 to 15 per cent aluminum, 12 to per cent nickel, about 5per cent copper if desired, and the remainder iron, such as is describedand claimed in Patents 1,947,274 and 1,968,569, issued February 13 andJuly 21, respectively, 1934, to William E. Ruder.

The fixed contact 25 is mounted upon a conducting strip 29 which passesthrough a slot in the wall of the casing ill to form with a bolt anexternal contact terminal. A second external contact terminal 3| isconnected to the movable contact 25 by means of a flexible conductinglead 32 attached to the terminal 3| and to the bolt 22. The bolt 22 isin electrically conducting engagement with the flexible contact spring23 and with the flexible conducting lead 32.

According to the preferred form of my invention illustrated in thedrawing, the expansible rod I5 is disposed in heat conducting relationto a hairpin type resistance heater 35. As shown, the resistance heater35 is closely adjacent and substantially parallel to the expansible rodl8 and has its electrically remote-ends extending through an aperture,in the wall or the casing l5 for electrical connection to a pair ofheater terminals 35 and 31. For electrical connection and mechanicalsupport one end of the heater 35 is welded to a plate 38a connected tothe heater terminal 35 and the other end of the heater 35 is welded to aconducting strap 33 connected to the heater terminal 31. In order topreclude accidental short circuiting oi the heater 35 a small strip ofinsulating material 39 may be inserted between the electrically remoteends 01' the heater 35 in the region of their connection to the externalterminals 35 and 31. The heater 35 is preferably connected in circuitwith a motor or other apparatus to be protected, so that it carries thesame current as that flowing through the protected circuit or a currentproportional thereto. The contacts 25, 25 are preferably arranged in acontrol circuit, as for example, in

, magnet will attract its keeper.

series with the actuating coil of a line contactor.

In order to provide adequate electrical insulation between separatecircuits as required by present day commercial standards. a strip offlexible insulating material 49 may be sprung into position betweensuitable bosses formed on the casing I5 and arranged to isolate theheater terminal 31 from the contacts 25, 26.

Simple means are provided for selectably arranging my thermal relay foreither manual or automatic reset. To this end I pivotally mount a resetlever or plate upon a screw 46 attached to the side wall oi! the casingI0. One end of the lever 45 is provided with an abutment 41 arranged toengage a slidable and manually operable reset pin 48 which projectsthrough one wall or the casing Ill. The opposite end of the lever 45 isarranged to provide a pair oi forwardly extending projections 45 and 49between which the spring strips 23 and 24 and the rigid portion 2| 0!the switch member i3 are disposed in spaced relation. The reset lever 45is also provided with a pin 50 extending through a slot 5| in the rearwall of the casing l9 and connected to one end of a substantiallystraight The wire 52 has in a slot 53 formed in the rear side of thecasing l5 and has its other end fixedly connected to the casing by meansof a screw 54. Within the slot 53 is moulded an upright boss 55 havingan appreciable thickness.

By comparing now Fig. 3 with Fig. 1, it will be observed that when thespring 52 is arranged upon the right side of the boss 55, as viewed atFig. 3, the reset lever 45 of Fig. 1 will be biased to its extremeclockwise position, as viewed in Fig. 1. In its tripped position theswitch member i3 is rotated counterclockwise so that the contact spring23 approaches the projection 45 of the reset lever 45 and the air gapbetween the magnet 25 and its keeper 21 is sufficiently great so thatthe force of magnetic attraction is unable to return the switch memberto contact closing position even though the rod l8 contracts. To resetthe relay the button 45 is depressed to rotate the reset lever 45counterclockwise until the pro ection 49 engages an adjustable stopscrew 55 mounted in the side of the base I5. I! the rod l5 has cooledsumciently to allow the switch member l3 to return to contact closingposition, the projection 45 on the reset lever 45 by engag mg the spring23 will move the switch member clockwise sufficiently to bring thekeeper 21 within the effective fleld of the magnet 25 and the If,however, the reset button 45 is depressed before the rod II has cooledand contracted sufficiently to permit the switch member i3 to return tocontact closing position, no reclosure will result. In this case theprojection 45 oi! the reset lever 45 will engage the contact spring 23between its point of support and the projection 24a and force the spring24 into engagement with the projection 2|a. Since the rigid portions ofthe switch member are held in fixed position by the expanded rod l5, theprojection 45 will bend the spring 23 into reverse configuration betweenthe bolt 22 and the projection 23, thereby preventing reclosure oi thecontacts. By the means described, reclosure of the contacts is preventeduntil the rod l5 has cooled sufllciently to permit the keeper 21 to moveinto engagement with the magnet 25. This is true even though the resetbutton 45 is held continuously depressed.

In order to" convert the relay for automatic reset operation it ismerely necessary to remove the screw 54 of Fig. 3 thereby to release thespring 52, and then to reconnect the spring 52 after placing it on theother side of the boss 55.

with the permanent magnet 28. v

In operation my thermal overload relay is normally in the position shownin Fig. l in which the expansible rod I8 is contracted and the switchmember i3 is rotated about the end l2 of the supporting rod II to itsextreme clockwise position in which the keeper 21 is in engagement withthe magnet 28 and the contacts 25 and 26 are also in engagement. Uponthe occurrence of an excessive current in the heater v 35 and theconsequent generation of an excessive amount of heat thereby, theexpansible rod l8 elongates and exerts a force tending to rotate theangular switch member IS in a counterclockwise direction about its pivotpoint upon the end l2 of the supporting rod ll. Such counterclockwisemovement is initially resisted by the magnetic attraction between thepermanent magnet 21 and its keeper 25. Eventually, however, the forceexerted upon the armature spring 24 by means of the small in-turnedprojection 2la on the rigid portion 2i of the switch member I3 issuflicient to pull the keeper 21 away from the magnet 28, therebypermitting the switch member l3 to rotate in a counterclockwisedirection. Since the magnet and keeper are disengaged with a snapaction. the armature spring 24 will move sufiiciently far when releasedso that the in-turned projection 24a on the end of the spring willengage the contactspring 23 with a hammer blow to disengage the movablecontact 25 from the stationary contact 26.

If the relay has been set eration the reset lever 45 will be biased in aclockwise direction and the movable switch member I! will remain in itsextreme counterclockwise position regardless of subsequent cooling andcontraction of the expansible rod l8. As has been previously explained,the device may be reset under these conditions by depressing the button48. If, on the other hand, the relay has been adjusted for automaticreset operation the reset lever 45 will be biased to its counterclockwise position as soon as the expansible rod i8 is suflicientlycooled to permit such movement.

While I have described but one preferred embodiment of my invention byway of illustration,

many further modifications will occur to those skilled in the art, and Itherefore wish to have it understood that I intend by the appendedclaims to cover all such modifications as fall within the true spiritand scope of my inventi-"n What I claim as new and desire to secure byLetters Patent of the United States is:

l. A thermosensitive switch comprising a support, a switch memberincluding a pair of fiex ible portions and a rigid portion connectedtogether in substantially parallel spaced relation, pivotal means formounting said switch member upon said support, circuit controlling meanscarried by a first of said flexible portions, snap acting means carriedby a second of said flexior manual reset op-' ible portions forreleasably retaining said second flexible portion in a predeterminednormal position, and t hermoresponsive means operable in conjunctionwith said rigid portion to release said snap acting means and to'movesaid second flexible portion into striking engagementwith said firstflexible portion thereby to actuate said circuit controlling means.

2. A thermosensitive switch comprising a base, a fixed contact mountedupon said base, a switch memberincluding a pair of flexible portions anda rigid portionvconnected together in substantially parallel spacedrelation, pivotal supporting means for said switch member, a movablecontact carried by a first of said flexible portions and arranged toengage said fixed contact, magnetic means carried by the second of saidflexible portions, second magnetic means 'on said base arranged normallyto releasably retain said first magnetic means and to bias said contactsinto engagement, and an expansible member arranged to rotate said switchmember about said pivotal supporting means, whereby said rigid portionengages said second flexible portion to release said first magneticmeans with a snap action and to move said second flexible portionintostriking engagement with said first flexible portion thereby todisengage said contacts.

3. A thermosensitive switch comprising a base, a fixed contact mountedupon said base, a movable switch member pivotally supported upon saidbase, said switch member including a pair of flexible portions and arigid portion connected together at one end and extending insubstantially parallel spaced relation, a movable contact mounted uponthe outer end of a first of said flexible portions and arranged toengage said fixed contact, magnetic means m'ounted upon the outer end ofa second of said flexible portions, the outer end of said secondflexible portion being formed to provide a first projection arranged toengage said first flexible portion adjacent said movable contact, secondmagnetic means on said base arranged to engage and releasably to retainsaid first magnetic means thereby to bias said contacts into engagement,a second projection on the outer end of said rigid portion for engagingsaid second flexible portion adjacent its end, and thermosensitiveexpansible right angular switch member having one leg including a pairof flexible portions and a rigid portion connected together insubstantially parallel spaced relation, a pair of relatively expansi'blerods disposed in substantially parallel spaced relation with each otherand with saidone leg between said base and the other leg of said switchmember, means for biasing said switch member into pivotal engagementwith said rods, circuit controlling means carried by a first of saidflexible portions, snap acting means carried by a second of saidflexible portions for releasably retaining said second flexible portionin a predetermined normal position, and means for heating atleast one ofsaid relatively expansible rods in proportion to the value of thecurrent in said circuit, whereby when said current attains secondflexible portion to release said snap acting means and to move saidsecond flexible por-- tion into engagement with said first flexibleportion with a hammer blow to actuate said circuit controlling means.

5. A thermosensitive switch for protecting an electric circuitcomprising a base of insulating material having a plurality of sidewalls, a fixed contact mounted upon one of said walls, a substantiallyright angular movable switch member having a rigid leg pivotally mountedupon a pair 01 relatively expansible rods, said rods being disposed insubstantially parallel spaced relation between a second of said wallsand said transverse leg and at least one of said rods being adjustablymounted upon said second wall, the other leg of said switch memberincluding a pair of flexible portions and a rigid portion connectedtogether at one end and extending in substantially parallel spacedrelation, a movable contact mounted upon the outer end of a first orsaid flexible portions and arranged to engage said fixed contact, akeeper of magnetizable material mounted upon the outer end of the secondof said flexible portions, the outer end 01' said second flexibleportion being formed to provide a first projection arranged to engagesaid first flexible portion adjacent said movable contact, a permanentmagnet mounted upon said one wall and arranged to engage and releasablyto retain said keeper thereby normally to bias said contacts intoengagement, a second projection on the outer end 01' said rigid portionengaging said second flexible portion adjacent said keeper, and meansresponsive to the current in said circuit for heating one of said rodsto rotate said switch member, whereby said rigid portion presses saidkeeper out 01 engagementwith said magnet with a snap action and saidfirst projection is moved into striking engagement with said flrstflexible membar to disengage said contacts.

6. A thermosensitive switch ior protecting an electric circuitcomprising a base of insulating material having a plurality oi sidewalls forming a container, a flxed contact mounted upon one of saidwalls, a substantially right angular movable switch member having a pair01' legs disposed in substantially parallel spaced relation to adjacentwalls of said container, a substantially nonexpansible supporting rodadjustably mounted in a wall adjacent said one wall of said base andextending inwardly therefrom, spring means for biasing one of said legsinto pivotal engagement with said supporting rod, an expansible roddisposed in substantially parallel spaced relation to said supportingrod and pivotally engaging said base and said one leg, the other leg orsaid switch member including a pair 01' flexible portions and a rigidportion connected together at one end and extending in substantiallyparallel spaced relation, a movable contact mounted upon the outer endof a first of said flexible portions and arranged to engage said flxedcontact, a keeper o1'.magnetizable material mounted upon the outer endof the second 01' said flexible portions, the outer end of said secondflexible portion being formed to provide a first projection arranged toengage said first flexible portion adjacent said movable contact, apermanent magnet mounted upon said base and arranged to engage andreleasably to retain saidkeeper thereby to bias said contacts intoengagement, a second projection on the outer end of said rigid portionengaging said second flexible portion adjacent its end, and electricheating means responsive to the current'in said circuit for heating saidexpansible rod, whereby said keeper is released from said magnet bypressing engagement of said second projection with said second flexibleportion and said second flexible portion is moved with a snap action tostrike said first flexible portion and to disengage said contacts.

7. A thermosensitive switch comprising a support, a switch memberincluding a pair of flexible portions and a rigid portion connectedtogether in substantially parallel spaced relation, pivotal means formounting said switch member upon said support, circuit controlling meanscarried by a first of said flexible portions, snap acting means carriedby a second of said flexible portions for releasably retaining saidsecond flexible portion in a predetermined normal position,thermoresponsive means operable in conjunction with said rigid portionto release said snap acting means and to move said second flexibleportion into striking engagement with said first flexible portionthereby to actuate said circuit controlling means, resetting meansarranged to engage said flexible portion and to move said switch memberto reset said circuit controlling means, and means operable inconjunction with said rigid portion of said switch member and with saidresetting means positively to prevent resetting of said circuitcontrolling means until s aid thermoresponsive means have cooled to apredetermined temperature.

8. A thermosensitive switch comprising a support, a switch memberincluding a pair of flexible portions and a rigid portion connectedtogether in substantially parallel spaced relation, pivotal means'formounting said switch member upon said support, circuit controlling meanscarried by a first of said flexible portions, said first flexibleportion having a predetermined normal curvature, snap acting meanscarried by a second of said flexible portions for releasably retainingsaid second flexible portion in a predetermined normal position,thermoresponsive means operable in conjunction with said rigid portionto release said snap acting means and to move said second flexibleportion into striking engagement with said flrst flexible portionthereby to actuate said circuit controlling means, resetting meansarranged to engage said flrst flexible portion intermediate its ends andthereby to move said switch member to reset said circuit controllingmeans, and means including said rigid portion for engaging the endsofsaid flexible portion to prevent resetting of said circuit controllingmeans until said thermoresponsive means has cooled to a predeterminedtemperature, whereby actuation of said resetting means prior to saidpredetermined cooling of said thermoresponsive member produces areversal of the curvature of said flrst flexible member therebypositively to prevent the resetting of said circuit controlling means.

9. A thermosensitive switch comprising a support, a switch memberincluding a pair of flexible portions'and a rigid portion connectedtogether in substantially parallel spaced relation, pivotal means formounting said switch member upon said support, circuit controlling meanscarried by a first of said flexible portions, snap acting means carriedby a second of said flexible portions for releasably retaining saidsecond flexible portion in a predetermined normal position,thermoresponsive means operable in conjunction with said rigid portionto release said snap acting means and to move said second flexible'portion into striking engagement with said first flexible portionthereby to actuate said circuit controlling means, manually operableresetting means ar-' away from said first flexible portion thereby to'provide automatic or manual resetting, respectively, of said circuitcontrolling means.

10. A thermosensitive switch comprising a support, a switch memberincluding a pair of flexible portions and a rigid portion connectedtogether in substantially parallel spaced relation, pivotal means formounting said switch member upon said support, circuit controlling meanscarried by a first of said flexible, portions, snap acting forreleasably retaining said second flexible por I tion in a predeterminednormal position, thermoresponslve 'means operable-in c'orLiunction' withsaid rigid ,portionto release said snap acting means and to movesaid'second flexible portion into striking engagement with said firstflexible portion thereby to actuate said circuit controlling means,manually operable resetting means arranged to engage first flexibleportion and to move said switch member to reset said circuit controllingmeans, spring means arranged selectably to bias 'said'resetting meanstoward or away 7 means carried by a second of said flexible portionsfrom said first flexible portion, and'a boss formed upon said casing andengaging said spring means

